What you say is true...but there are many folks, not particularly religious folks, who have pondered the idea that what we know as ET is demonic.

Here are a few quotes (Whitley Strieber is/was an agnostic and Jacques Vallee is a non-religious physicist):

"I felt an absolutely indescribable sense of menace. It was hell on earth to be there [in the presence of the entities], and yet I couldn't move, couldn't cry out, couldn't get away. I'd lay as still as death, suffering inner agonies. Whatever was there seemed so monstrously ugly, so filthy and dark and sinister. Of course they were demons. They had to be. And they were here and I couldn't get away." - Whitley Strieber, Transformation, p. 181

"Increasingly I felt as if I were entering a struggle that might even be more than life and death. It might be a struggle for my soul, my essence, or whatever part of me might have reference to the eternal. There are worse things than death, I suspected... so far the word demon had never been spoken among the scientists and doctors who were working with me...Alone at night I worried about the legendary cunning of demons ...At the very least I was going stark, raving mad." - Whitley Strieber, Transformation, p. 44-45

"The 'medical examination' to which abductees are said to be subjected, often accompanied by sadistic sexual manipulation, is reminiscient of the medieval tales of encounters with demons. It makes no sense in a sophisticated or technical framework: any intelligent being equipped with the scientific marvels that UFOs possess would be in a position to achieve any of these alleged scientific objectives in a shorter time and with fewer risks." - Dr. Jacques Vallee, Confrontations, p. 13

"The symbolic display seen by the abductees is identical to the type of initiation ritual or astral voyage that is imbedded in the [occult] traditions of every culture...the structure of abduction stories is identical to that of occult initiation rituals...the UFO beings of today belong to the same class of manifestation as the [occult] entities that were described in centuries past." -Dr. Jacques Vallee citing the extensive research of Bertrand Meheust [Science-Fiction et Soucoupes Volantes (Paris, 1978); Soucoupes Volantes et Folklore (Paris, 1985)], in Confrontations, p. 146, 159-161

You’re only commenting on abductions, not UFO sightings. The violent nature of abductions by unusual creatures would produced those feelings. I can only imagine how and alien would view it, if nazis had gone to another world. But that wouldn’t make the nazis demons, only evil.
As for demonic actions, like the sexual reports. Many believers view other religions as demonically influenced, which would include evil behavior such as sexual abductions. Alien religions, if any, would not likely be based on Christ, and therefore likely a form of devil worship. What’s kind of behavior do you expect from alien sinners?
And there are reports in sightings of more than one race. Some have been seen as fairly benign, and only the more aggressive and curious would risk and physical encounter. Whatever they are, judging the actions of one group to represent them all is risky.
Most sightings are mistaken events, easily explained away. Some are hoaxes. But many are buy reputable people. I’m certain and air force or airline pilot can recognize a ship. And most of what is going on doesn’t resemble biblical demonic activity. That usually involved posession, not abduction.
I would suggested looking at Medieval accounts be done with a grain of salt. Everything they didn’t understand was deamed demonic and embellished in stories.